1. Field of the Invention
This invention generally relates to apparatus using television cameras to inspect the surface of an object, and more particularly to apparatus using television cameras to detect the initiation and growth of fatigue cracks in a test specimen. Thus the fatigue failure of a test specimen can be observed and recorded for study without the need for an operator to be present throughout the duration of the tests.
2. Description of the Prior Art
The use of television cameras to inspect an object whose surface changes with respect to time or which is moving rapidly are well known. U.S. Pat. No. 3,111,555, for example, teaches an apparatus which uses a television camera to permit visual inspection of the surface of a rapidly moving metal strip. Similarly, U.S. Pat. No. 3,176,306 uses a television camera to detect imperfections on the surface of a rapidly moving tin sheet. In other applications, a television camera has been used in apparatus designed for analyzing sprays as in U.S. Pat. No. 3,275,744; counting and measuring small particles as in U.S. Pat. No. 3,390,229; and for determining the dimensions of a rapidly moving object as in U.S. Pat. No. 3,666,885. Typical of other devices using a television camera are U.S. Pat. Nos. 3,294,002 and 3,679,823.
While these earlier developments use a television camera to view a moving object, they lack the aspects of the present invention wherein a plurality of television cameras are used to record the initiation and growth of a fatigue crack in a test specimen. In addition, the prior art uses of a television camera are limited to those instances in which the sequence of lighting and photographing the object can be timed to coincide with the persistence time of the existing vidicon tube of the camera.
It is therefore an object of the present invention to provide an apparatus for detecting surface cracks in fatigue specimens.
The further object of the present invention is an apparatus for making a visual recording of the initiation and propagation of fatigue cracks.
These and other objects of the invention will be readily apparent when considered in reference to the description and claims and taken in connection with the attached drawings to which they relate.